It is proposed to investigate the cellular and subcellular events that result from activation of thymus-derived lymphocytes (T-cells). The biochemical and biophysical characteristics of the subpopulations of unactivated and activated T-cells will be correlated with their functional activities. Furthermore, the sensitivities (radiosensitivity; inhibitors of DNA, RNA, and protein synthesis; heavy metals; chemicals such as cortisone, iodoacetamide, and penicillamine) of the T-cell subsets will be examined in terms of the differential effects of various reagents on the structure(s) versus the function(s) of the T-cell subpopulation. Specific emphasis will be placed on the changes of the T-cell's plasma membrane. Fluctuations in helper activity (specific and nonspecific) and suppressor activity will be quantitated and compared to alterations in the quantity of surface antigens defined by specific alloantisera, the glycoprotein content of the membranes, various enzyme activities of the membranes, and the membrane and intracellular concentrations of protein and nonprotein thiols. The role of sulfhydryl yields (reversibly) disulfide interplay in the activation process will be assessed. T-cells must undergo some form of differentiation or development in order to become activated; the physiological T-cell changes which result from this activation may be due to quantitative or qualitative changes. Information obtained by comparing unprimed T-cells and activated T-cells will be used to investigate the mechanisms involved in the regulation of T-cell activation especially in regard to macrophage activities. Correlation of the biologic and biomolecular aspects of the T-cell subpopulations will aid in understanding the sensitivities and regulatory mechanisms of T-cells.